IP-Based Video Technology
March 1, 2007
Coaxial cable-based analog video systems have been the mainstay of security CCTV for many years, providing viewing and storage of video for a wide range of applications. Recently a new breed of IP-based CCTV systems has emerged that uses UTP (unshielded twisted pair) cabling and standard data network technology in place of the tried and true coaxial cable. It is a technology that has been around for some time for data networking, but only recently has it become embraced by manufacturers, end users and security dealers for video applications. These IP-based systems are not to be confused with hybrid systems that allow traditional analog CCTV cameras to be connected to a data network. Rather, IP-based systems refer to a CCTV system that is entirely IP-based. As with any new technology there is a learning curve â€” and frequent myths associated with the technology. These will be overcome as the systems evolve, dealers begin offering IP-based CCTV systems, and end users understand the advantages of this technology.
To help dispel some of the misconceptions associated with IP-based systems, SDM explains the various differences between analog CCTV systems and IP-based CCTV systems and provides a clear view of what comprises an IP-based video system.
System ExpansionThe capacity of a traditional analog system is determined by the number of inputs available on the multiplexer or recorder hardware â€” typically available in 4, 8, 9, 16, or 32 camera configurations. If the original system is based upon a 16-camera recorder, adding camera 17 requires either replacing the old 16-camera unit with a new 32-camera unit or adding a second recorder. IP-based systems are not subject to such limitations. The number of cameras that can be connected to an IP-based system can frequently be increased by purchasing another license as long as the storage space is adequate. Increasing storage space is also easier with IP-based systems since traditional analog recorders are limited by the manufacturer-determined size of the hard drive or, in the case of a VCR, by the tape itself. IP-based recorders can use any standard network storage device so dealers can increase the amount of time that video can be stored by adding off-the-shelf network storage devices or archival storage devices.
Wiring RequirementsA traditional analog camera CCTV system with a DVR requires a coaxial cable home run for the video signal for each camera, with additional cables for power, and PTZ control if used. This is very labor intensive and combined with the cost of the cables required, quickly results in a significant upfront expense. Adding cameras to the system requires more home run cables and possibly replacing the DVR if there are insufficient inputs available. Alterations to analog CCTV systems can also be a problem since coaxial cable should not be spliced, so moving a camera often requires that a cable be run from the new location back to the recorder.
IP-based systems use standard Cat 5e or better UTP, which is frequently installed as part of the basic data network infrastructure. Installing an IP-based system allows the CCTV system to utilize any existing unused cables and possibly even the existing data network hardware such as switches, minimizing the initial cost to install the video system and enhancing the return on investment for the data network. This approach is not always an all-in-one process but may include using portions of the existing infrastructure and adding dedicated video equipment and cables as necessary. Since IP-based systems allow the use of all standard data network topologies, a technician can even use wireless nodes for the transmission of images where running of cables is cost-prohibitive.
The figure, “IP CCTV System” provides an overview of an IP-based camera system with a networked digital recorder. The first obvious difference is the reduction in cabling required. With an IP-based system, a single Cat 5e or better cable is run from each camera to a centralized hub or switch, which then combines all of the video for transport across the network to the recorder and for viewing. It is possible to use a single data cable not only for video and PTZ control, but also to supply power to the camera.
This savings is even more readily apparent when the cameras are located on multiple floors as shown in the figure titled, “Distributed IP CCTV System.” If this were a traditional analog system the coaxial cables from every camera would have to be run from each camera to the recorder, along with the associated power and PTZ cables. Keep in mind that data cables such as Cat 5e have a maximum length of 100 meters, before entering a switch or repeater to amplify the signal. The single data cable is smaller than a traditional RG-59U coaxial cable and since no additional cables are required for PTZ, audio, and possibly power, the size of the cable bundle is also smaller, allowing smaller penetrations in walls and floors or conduit.
CamerasThe cameras used by IP-based video systems are much more sophisticated than their analog siblings, which helps explain why they are more expensive. The resolution of analog cameras is limited by the NTSC/PAL specifications, to approximately 0.4 megapixels at 4CIF (common intermediate format) with a resolution of 704 by 576. IP-based cameras have no such limitations and megapixel or better resolutions are possible.
IP cameras frequently have input and output connections that can be used to increase the flexibility of the system. For example, an installer could connect a door contact or motion detector to the input and, when activated, the contact or motion detector can command the camera to send video to the recorder or to increase the FPS â€” once again reducing the burden placed on the data network during non-alarm times. The outputs of IP cameras can be used to activate a local device when the input is tripped or when the camera detects motion.
BandwidthBandwidth is the amount of data that passes through a network and is generally expressed as Megabits (Mb) or Gigabits (Gb) for newer networks. The very common 10/100 Mb network provides 10 or 100 Megabits of data per second (Mbps), and newer networks are 1,000 Mb. The figure titled, “Estimated Bandwidth Usage,” shows the amount of bandwidth that a typical video system can require based upon the image size and images per second. The actual bandwidth required depends upon the ability of the compression technique to reduce the file size, the resolution of the images, and the images per second. In addition to having a dramatic effect on bandwidth, lowering the resolution or images per second also can reduce the overall image quality.
Adding a large number of cameras to a 10/100 Mb network can quickly use up the available throughput which can result in the slowing down of all network functions â€” and a very unhappy IT manager. These problems can be addressed by placing the IP cameras on a dedicated parallel network or possibly by placing the cameras on a single network segment. In a parallel network, installers may be able to use the unused horizontal cable runs from the data closet to the cameras and between floors; rather than utilize the existing network switches, installers use switches that are used exclusively for the video system, and connect this parallel network to the client’s existing network for remote viewing. In a parallel network installers are responsible for all video network administration, as well as the installation and servicing of devices, and addressing.
Another new approach to network bandwidth utilization is to store the video images at the camera and then send them to the network storage device either on a demand basis or at a pre-determined time when normal network usage is very low, such as early in the morning.
Remote ConnectionsNot all broadband connections are created equal â€” each has its own throughput, which should be considered when designing a system with remote viewing functions. The figure “Broadband Speed Comparison,” shows a basic comparison of the approximate speeds of the most common broadband connections. It should be noted that some connections do not provide the same speed in both directions.
For example, DSL lines typically are designed to provide a high rate of transfer for downloading and a much lower rate for uploading. This difference can be as much as a factor of 10, which means that if a customer is using a DSL line at both ends, the receiving end can receive data 10 times as fast as the transmitting unit can send it, effectively limiting the overall speed to that of the upload capacity. It is important that dealers and systems integrators are fully versed in the nuances of network topography and the proper methods to install and test IP devices and the network hardware the devices utilize. Errors can be very embarrassing and costly to correct after the fact.